Fluid flow rate is the quantification of bulk fluid or gas movement, typically measured as volumetric and mass flow rates. The ability to measure reliably and accurately fluid flow rates serves an important function in a variety of processes and industries (e.g., chemical processing, oil and gas transport and production, etc.). An orifice fitting is one of many devices that may be used to measure volumetric or mass flow rate of fluids flowing through a pipe or conduit. An orifice fitting typically employs a flat, thin plate having a central orifice that is smaller in diameter than the diameter of the conduit in which the plate is disposed. The orifice plate is positioned between a sealing ring and a compression ring that may be held together by a fastener to form an orifice plate assembly. The orifice plate assembly is disposed within a plate carrier, which is, in turn, supported and aligned within the orifice fitting. In this arrangement, the mass fluid flow rate through the conduit may be calculated from the pressure differential measured across the orifice plate, as well as other parameters.
When using an orifice fitting to measure fluid flow, many factors must be considered in order to obtain accurate flow estimates. Typically, the orifice plate assembly is positioned within the orifice fitting with the seal and compression rings positioned on the upstream and downstream sides, respectively, of the orifice plate. A seal is provided between the seal ring and orifice plate, but no seal is provided between the orifice plate and the compression ring. With these unidirectional orifice plate assemblies, leakage may occur if the compression ring side of the orifice plate assembly is inadvertently positioned upstream. Leakage results in reduced pressure drop across the orifice plate and inaccurate estimations of fluid flow through the fitting.